1. Field of the Invention
The present invention relates to a battery back apparatus having a battery pack composed of a plurality of rechargeable batteries, in which the temperature of each of the rechargeable batteries is regulated stably and uniformly.
2. Description of the Related Art
In a battery pack composed of a plurality of rechargeable batteries, in order to prevent increase in the temperature of each rechargeable battery caused by heat generated by charge/discharge of the rechargeable battery and thus prevent decrease in a battery power, charge/discharge efficiency, and a battery life, it is conventionally known that the rechargeable batteries are arranged in parallel with cooling medium passages interposed therebetween and a cooling medium supply device is provided for supplying a cooling medium to the cooling medium passages (see Japanese Patent Laid-Open Publication No. 2001-167803, for example).
It is also known that four side faces of a battery pack that has six side faces are thermally insulated by heat insulation material while the remaining two side faces are cooled (see Japanese Patent Laid-Open Publication No. Hei 7-192774, for example).
Moreover, it is also known that a case is provided for accommodating a plurality of rechargeable batteries while contacting the rechargeable batteries at their circumferential surfaces to be thermally coupled. The outer circumferential surface of the case is covered with heat insulation material, and a heat pipe for dissipating heat transferred to the case to the outside is provided on a wall surface of the case, (see Japanese Patent Laid-Open Publication No. 2001-76771).
In the configuration disclosed in Japanese Patent Laid-Open Publication No. 2001-167803, it is possible to cool the respective rechargeable batteries relatively efficiently and uniformly because they are cooled by making the cooling medium flow in the cooling medium passages between them. However, the rechargeable batteries are affected by radiation heat from sunlight and heat radiated from an automotive exhaust pipe and are also affected by the surrounding temperature greatly. Thus, it is difficult to keep the rechargeable batteries at a predetermined temperature stably and uniformly. Further, there is another problem in which heat efficiency is not good.
The configuration disclosed in Japanese Patent Laid-Open Publication No. Hei 7-192774 has the following problem. In this configuration, four side faces of the battery pack are covered with the heat insulation material while only the remaining two side faces are cooled. Although this configuration is hardly affected by heat from the outside, cooling capacity is low and uniform cooling cannot be achieved. Thus, the temperature of the rechargeable battery increases particularly around the center of the battery pack, resulting in a decreased battery life.
In the configuration disclosed in Japanese Patent Laid-Open Publication No. 2001-76771, heat of the rechargeable batteries accommodated in the case covered with the heat insulation material is dissipated to the outside of the case by means of the heat pipe. This configuration is hardly affected by heat from the outside. However, if it is tried to achieve the cooling capacity that can cool all the rechargeable batteries effectively only by using the heat pipe, a number of heat pipes, and a large amount of heat collecting material are necessitated. This reduces space efficiency and increases the cost. Nevertheless, it is difficult to uniformly cool the respective parts of the rechargeable batteries.